Pixel circuit outputting pulse width signal and optical sensor using the same

ABSTRACT

There is provided a pixel circuit for performing analog operation including a photodiode, a first temporal circuit, a second temporal circuit and an operation circuit. Within a first interval, the photodiode detects first light energy to be stored in the first temporal circuit. Within a second interval, the photodiode detects second light energy to be stored in the second temporal circuit. Within an operation interval, the first temporal circuit outputs a first detection signal having a first pulse width according to the first light energy and outputs a second detection signal having a second pulse width according to the second light energy for being calculated by the operation circuit.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 18/071,477 filed on Nov. 29, 2022, which is acontinuation application of U.S. patent application Ser. No. 17/672,028filed on Feb. 15, 2022, which is a continuation application of U.S.patent application Ser. No. 17/009,417 filed on Sep. 1, 2020, the fulldisclosures of which are incorporated herein by reference.

To the extent any amendments, characterizations, or other assertionspreviously made (in this or in any related patent applications orpatents, including any parent, sibling, or child) with respect to anyart, prior or otherwise, could be construed as a disclaimer of anysubject matter supported by the present disclosure of this application,Applicant hereby rescinds and retracts such disclaimer. Applicant alsorespectfully submits that any prior art previously considered in anyrelated patent applications or patents, including any parent, sibling,or child, may need to be re-visited.

BACKGROUND 1. Field of the Disclosure

This disclosure generally relates to a pixel structure and, moreparticularly, to a pixel circuit capable of outputting pulse widthsignals corresponding to detected light energy and performing analogoperation.

2. Description of the Related Art

Nowadays, the optical sensor outputs voltage values to be converted to adigital image frame by an analog-to-digital converter, and then aprocessor of the optical sensor performs the following operation usingthe digital image frame, e.g., calculating displacement or performingmotion detection.

However, in an optical sensor performing the operation in a digitalbackend thereof, the digital backend generally needs frame buffers tostore the whole digital image frame. Generally, the optical sensor needstwo frame buffers to store pixel data.

Accordingly, it is necessary to provide a pixel structure that performsvarious operations on pixel data at analog phase.

SUMMARY

The present disclosure provides a pixel circuit that represents detectedlight intensity using a pulse width, and performs the pixel-wiseoperation, including intra-pixel and inter-pixel operations, using pulsewidth signals.

The present disclosure provides a pixel circuit including a photodiodeand a temporal circuit. The temporal circuit is coupled to thephotodiode and includes a capacitor, a first transistor, a secondtransistor and a third transistor. The capacitor has a first end coupledto the photodiode. A source of the first transistor is connected to avoltage source and a drain of the first transistor is connected to anode. The second transistor is coupled between a second end of thecapacitor and the node. The third transistor is coupled between the nodeand a ground voltage, and a controlled terminal thereof being coupled tothe second end of the capacitor.

The present disclosure further provides an optical sensor including aphotodiode, a first temporal circuit and a second temporal circuit. Thephotodiode is configured to generate light energy. The first temporalcircuit and the second temporal circuit are both coupled to thephotodiode and respectively configured to store the light energy withindifferent time intervals. Each of the first temporal circuit and thesecond temporal circuit includes a capacitor, a first transistor, asecond transistor and a third transistor. The capacitor has a first endcoupled to the photodiode. The first transistor is coupled between avoltage source and a node, and a controlled terminal of the firsttransistor is configured to receive a control signal for converting thelight energy stored in the capacitor to a detection signal. The secondtransistor is coupled between the node and a second end of thecapacitor. The third transistor is coupled between the node and a groundvoltage, and a controlled terminal thereof being connected to the secondend of the capacitor.

The present disclosure further provides an optical sensor including aphotodiode, a first temporal circuit and a second temporal circuit. Thephotodiode is configured to generate light energy. The first temporalcircuit and the second temporal circuit are both coupled to thephotodiode and respectively configured to convert the light energywithin different time intervals to pulse width signals. Each of thefirst temporal circuit and the second temporal circuit includes acapacitor, a first transistor, a second transistor and a thirdtransistor. The capacitor has a first end coupled to the photodiode. Asource of the first transistor is connected to a voltage source and adrain of the first transistor is connected to a node. The secondtransistor is coupled between the node and a second end of thecapacitor. The third transistor is coupled between the node and a groundvoltage, and a controlled terminal thereof being connected to the secondend of the capacitor.

The temporal circuit of the present disclosure is used to store detectedlight energy of different time intervals and to output detection signalsof different pulse widths, wherein the pulse width is positively relatedto the detected light energy.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic block diagram of a pixel structure of an opticalsensor according to one embodiment of the present disclosure.

FIG. 2 is a circuit diagram of a pixel circuit according to oneembodiment of the present disclosure.

FIG. 3 is a circuit diagram of a temporal circuit of a pixel circuitaccording to one embodiment of the present disclosure.

FIG. 4A is an operational timing diagram of the temporal circuit in FIG.3 .

FIG. 4B is an operational timing diagram of the pixel circuit in FIG. 2.

FIG. 5 is a circuit diagram of a subtraction circuit of a pixel circuitaccording to one embodiment of the present disclosure.

FIG. 6 is a circuit diagram of an addition circuit of a pixel circuitaccording to one embodiment of the present disclosure.

FIG. 7 is a circuit diagram of an absolute difference circuit of a pixelcircuit according to one embodiment of the present disclosure.

FIG. 8 is a circuit diagram of a recursive circuit of a pixel circuitaccording to one embodiment of the present disclosure.

FIG. 9 is an operational timing diagram of the recursive circuit in FIG.8 .

FIG. 10 is a schematic diagram of one application of a pixel circuitaccording to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

The present disclosure is related to a pixel circuit that performspixel-wise analog operation. Every pixel outputs a detection signalhaving a pulse width corresponding to detected light energy. Anoperation circuit is used to perform the analog operation on the pulsewidth (PW) signals. The voltage value after the analog operation isfurther converted to a PW signal using a voltage-temporal conversioncircuit at first and then a next analog operation is performed by thesame or by another operation circuit. In this way, all data operation isaccomplished in the analog phase without being converted to digital dataat first.

Referring to FIG. 1 , it is a schematic block diagram of a pixelstructure of an optical sensor (e.g., CMOS image sensor) according toone embodiment of the present disclosure. The pixel structure includes apixel circuit 10 and an operation circuit 12. The pixel circuit 10 isused to output detection signals of different time intervals, e.g.,signals A and B in FIG. 1 indicating different detection signalsdetected within different time intervals. In the present disclosure, thedetection signals A and B respectively indicate magnitude of lightenergy detected by the pixel circuit 10 using pulse widths T1 and T2,wherein when the detected light energy is larger, the pulse width of thecorresponding detection signals A or B is longer.

The operation circuit 12 includes any circuit used to perform theoperation between signals, e.g., described by a subtraction circuit inFIG. 5 , an addition circuit in FIG. 6 and an absolute differencecircuit in FIG. 7 herein, but not limited thereto. In a pixel arrayincluding multiple pixels, the operation circuit 12 is arranged insideeach pixel to process data in the pixel or arranged between pixels toprocess data between pixels.

In some aspects, the pixel structure further includes an identifycircuit 14. The identify circuit 14 includes, for example, a comparatorfor comparing the output result of the operation circuit 21 with apredetermined threshold so as to identify an operating state of a deviceadopting the pixel structure of the present disclosure. For example,when the pixel structure of the present disclosure is adapted to a mousedevice, the identify circuit 14 is used to identify whether the mousedevice is lifted up by a user. The output result of the operationcircuit 12 indicates a brightness variation. When the identify circuit14 identifies that the brightness variation is larger than or smallerthan a brightness threshold, the mouse device is identified to be liftedby the user. The identify circuit 14 then outputs a control signal toperform corresponding controls, e.g., turning off the light sourceand/or not outputting displacement signals, but not limited to.

Please referring to FIG. 2 , it is a circuit diagram of a pixel circuit200 according to one embodiment of the present disclosure. The pixelcircuit 200 is used to output pulse width (PW) signals A and B, i.e.detection signals. The pixel circuit 200 includes a photodiode PD, atransfer transistor SWt, a reset transistor SWrst, a first temporalcircuit 2 a and a second temporal circuit 2 b all connected to a nodeV_(FD).

The photodiode PD is used to generate light energy according to thelight L being received. The light energy is respectively stored in thefirst temporal circuit 2 a and the second temporal circuit 2 b withindifferent time intervals (e.g., controlled by a control signal TX). Inthe present disclosure, in addition to storing light energy detectedwithin different time intervals, the first temporal circuit 2 a and thesecond temporal circuit 2 b further respectively convert the storedlight energy into detection signals A and B having corresponding pulsewidths (e.g., T1 and T2) for the operation circuit 12 to perform analogoperation. The first temporal circuit 2 a and the second temporalcircuit 2 b have identical circuit arrangement only being operatedwithin different time intervals.

The first temporal circuit 2 a stores first light energy (e.g.,referring to V_(SIG1) shown in FIG. 4B), generated by the photodiode PDwithin a first interval (e.g., referring to T_(SA) shown in FIG. 4B),and outputs a first detection signal A having a first pulse width T1according to the first light energy V_(SIG1) within an operationinterval (e.g., referring to T_(O1) shown in FIG. 4B).

The second temporal circuit 2 b stores second light energy (e.g.,referring to V_(SIG2) shown in FIG. 4B) generated by the photodiode PDwithin a second interval (e.g., referring to T_(SB) shown in FIG. 4B),and outputs a second detection signal B having a second pulse width T2according to the second light energy V_(SIG2) within the operationinterval T_(O1). It is appreciated that lengths of T1 and T2 in drawingsare only intended to illustrate but not to limit the present disclosure.

The reset transistor SWrst is coupled between a voltage source V_(DD)and the node V_(FD), and used to reset the first temporal circuit 2 a inthe first interval T_(SA) and reset the second temporal circuit 2 b inthe second interval T_(SB).

The transfer transistor SWt is coupled between the photodiode PD and thenode V_(FD), and used to transfer the first light energy V_(SIG1) to bestored into the first temporal circuit 2 a in the first interval T_(SA)and transfer the second light energy V_(SIG2) to be stored into thesecond temporal circuit 2 b in the second interval T_(SB). In this way,the pixel circuit 200 stores detected light energy of different timeintervals to indicate the variation of detected light with time.

In some aspects, the first temporal circuit 2 a further includes a firstinverter INV1 coupled between an output terminal of the first temporalcircuit 2 a and the operation circuit 12, and the first inverter INV1 isused to invert a phase of the first detection signal A; the secondtemporal circuit 2 b further includes a second inverter INV2 coupledbetween an output terminal of the second temporal circuit 2 b and theoperation circuit 12, and the second inverter INV2 is used to invert aphase of the second detection signal B. In other aspects, the firstinverter INV1 and the second inverter INV2 are arranged in the operationcircuit 12 instead of being arranged in the first temporal circuit 2 aand the second temporal circuit 2 b.

Please referring to FIGS. 3 and 4A, FIG. 3 is a circuit diagram of thetemporal circuit (e.g., 2 a and 2 b) of a pixel circuit according to oneembodiment of the present disclosure; and FIG. 4A is an operationaltiming diagram of the temporal circuit 2 a/2 b in FIG. 3 . It should bementioned that although FIG. 2 shows that a single pixel circuitincludes two temporal circuits, but the present disclosure is notlimited thereto. In other aspects, each pixel circuit includes a singletemporal circuit as shown in FIG. 3 to output a PW signal A or B.

In the present disclosure, operation of the temporal circuits 2 a and 2b in FIG. 2 is described using FIGS. 3 and 4A.

The temporal circuits 2 a and 2 b respectively include a storagecapacitor C, a first transistor SW1, a second transistor SW2 and a thirdtransistor SW3. The storage capacitors and the first to thirdtransistors are indicated by different reference numerals in FIG. 2 toindicate belonging to different temporal circuits.

A first end of the storage capacitor C (shown as a first capacitor C1 inthe first temporal circuit 2 a and as a second capacitor C2 in thesecond temporal circuit 2 b) is coupled to the reset transistor SWrst.The storage capacitor C is used to store light energy generated by thephotodiode PD, e.g., the first light energy V_(SIG1) or the second lightenergy V_(SIG2).

The first transistor SW1 (shown as SWa1 in the first temporal circuit 2a and as SWb1 in the second temporal circuit 2 b) is coupled between thevoltage source V_(DD) and a node Vx, and is controlled by a controlsignal BIAS (shown as BIAS1 in the first temporal circuit 2 a and asBIAS2 in the second temporal circuit 2 b) to convert the stored lightenergy to a detection signal, e.g., the first detection signal A or thesecond detection signal B.

The second transistor SW2 (shown as SWa2 in the first temporal circuit 2a and as SWb2 in the second temporal circuit 2 b) is coupled between thestorage capacitor C and the first transistor SW1, and controlled by acontrol signal AZ (shown as AZ1 in the first temporal circuit 2 a and asAZ2 in the second temporal circuit 2 b). In the first interval T_(SA),the second transistor SWb2 is not conducted to avoid changing the storedenergy in the second capacitor C2; and in the second interval T_(SB),the first transistor SWa2 is not conducted to avoid changing the storedenergy in the first capacitor C1.

The third transistor SW3 (shown as SWa3 in the first temporal circuit 2a and as SWb3 in the second temporal circuit 2 b) is coupled between asecond end of the storage capacitor C and a ground voltage.

Please referring to FIG. 4A again, it shows that operation of thetemporal circuit 2 a/2 b includes a reset interval, a charge transferinterval, a charge storage interval and a pulse width (PW) convertinterval. In the reset interval, control signals BIAS, RESET and AZ arerespectively at a high voltage level to reset charges on the storagecapacitor C, e.g., a voltage of the node V_(FD) being reset to V_(RESET)(e.g., equal to V_(DD)) and a voltage of the node V_(G) being reset toV_(AZ). In the charge transfer interval, the control signal RESET ischanged to a low voltage level, and when the control signal TX ischanged to a high voltage level, the light energy V_(SIG) detected bythe photodiode PD is transferred to the node V_(FD) via the transfertransistor SWt to cause the voltage thereon to decrease toV_(RESET)−V_(SIG), wherein V_(SIG) indicates the detected light energy.In the charge storage interval, the control signal RESET is changed tothe high voltage level again and the control signals BIAS and AZ arechanged to low voltage levels to store the light energy V_(SIG) to thenode V_(G) to cause the voltage thereon to increase to V_(AZ)+V_(SIG).Meanwhile, if the control signal AZ is kept at the low voltage level toturn off the second transistor SW2, charges stored in the storagecapacitor C are substantially kept constant.

In FIG. 4A, the reset interval, the charge transfer interval and thecharge storage interval as a whole is used as an energy storage intervalT_(SA) of the first temporal circuit 2 a or an energy storage intervalT_(SB) of the second temporal circuit 2 b. Before the operation circuit12 starts to operate, the first temporal circuit 2 a and the secondtemporal circuit 2 b sequentially store light energy detected by thephotodiode PD. As shown in FIG. 4A, till the PW convert interval isentered after the operation starts, the first light energy V_(SIG1) inthe first temporal circuit 2 a is converted to the first detectionsignal A and the second light energy V_(SIG2) in the second temporalcircuit 2 b is converted to the second detection signal B.

In the PW convert interval, the control signal BIAS uses a ramp signalhaving the voltage level decreasing with time. When the control signalBIAS starts at a high voltage level (e.g., V_(BIAS_AZ)), the current I1flowing through the first transistor SW1 is smaller than the current I3flowing through the third transistor SW3 to cause an output voltage ofVx to have a low voltage level. With the level decreasing of the controlsignal BIAS, the current I1 is increasing correspondingly, and when thecurrent I1 is substantially identical to the current I3, the outputvoltage of Vx changes to a high voltage level to form a negative PWsignal. After the output voltage of Vx passes an inverter INV, apositive PW signal is generated as shown in FIG. 4A, wherein a pulsewidth ΔT is positively related to the light energy V_(SIG). In this way,the temporal circuits 2 a and 2 b of the present disclosure convertlight energy detected by the photodiode PD to a timing signal to beoperated by the operation circuit 12.

Please referring to FIG. 4B, it is an operational timing diagram of thepixel circuit 200 in FIG. 2 . The first temporal circuit 2 a storesfirst light energy V_(SIG1) in the first capacitor C1 in the firstinterval (e.g., the energy storage interval T_(SA)) using the operationof FIG. 4A. The second temporal circuit 2 b stores second light energyV_(SIG2) in the second capacitor C2 in the second interval (e.g., theenergy storage interval T_(SB)) using the operation of FIG. 4A. Next, inthe first operation interval T_(O1), the first temporal circuit 2 a usesa ramp signal having the voltage level decreasing with time as thecontrol signal BIAS1 to convert the first light energy V_(SIG1) into afirst detection signal A; meanwhile, the second temporal circuit 2 buses a ramp signal having the voltage level decreasing with time as thecontrol signal BIAS2 to convert the second light energy V_(SIG2) into asecond detection signal B. Preferably, the ramp signals BIAS1 and BIAS2are substantially in-phase to generate detection signals A and Bsubstantially at the same time, but not limited thereto. It is possiblethat detection signals A and B are generated sequentially depending onthe operation of the operation circuit 12. The operation circuit 12performs the numerical calculation on the first detection signal A andthe second detection signal B in the first operation interval T_(O1),e.g., the summation, subtraction and absolute differencing given in thepresent disclosure, but the present disclosure is not limited to theseoperations.

As shown in FIG. 4B, in the first operation interval T_(O1), the firstinterval T_(SA) for storing the first light energy V_(SIG1) is prior tothe second interval T_(SB) for storing the second light energy V_(SIG2).

In one aspect, after the first operation interval T_(O1) is over, thesecond temporal circuit 2 b continuously holds the second light energyV_(SIG2), but the first temporal circuit 2 a stores a next first lightenergy V_(SIG1)′ in the first capacitor C1 in a next energy storageinterval T_(SA)′ also using the operation of FIG. 4A. Next, in a secondoperation interval T_(O2), the first temporal circuit 2 a uses a rampsignal having the voltage level decreasing with time as the controlsignal BIAS1 to convert the first light energy V_(SIG1)′ into a firstdetection signal A′; meanwhile, the second temporal circuit 2 b uses aramp signal having the voltage level decreasing with time as the controlsignal BIAS2 to convert the second light energy V_(SIG2) into a seconddetection signal B, which is substantially identical to that generatedin the first operation interval T_(O1). The operation circuit 12performs the numerical calculation on the first detection signal A′ andthe second detection signal B in the second operation interval T_(O2).In the second operation interval T_(O2), the first interval T_(SA)′ forstoring the first light energy V_(SIG1)′ is behind the second intervalT_(SB) for storing the second light energy V_(SIG2).

In the next energy storage interval, the first light energy V_(SIG1)′ inthe first temporal circuit 2 a is maintained, but the second lightenergy in the second temporal circuit 2 b is updated to V_(SIG2)′. Byalternatively updating the light energy stored in the first temporalcircuit 2 a and the second temporal circuit 2 b as shown in FIG. 4B, itis possible to perform the numerical calculation on signals of differenttime intervals.

Please referring to FIG. 5 , it is a circuit diagram of a subtractioncircuit 500 according to one embodiment of the present disclosure, whichhas two inputs respectively coupled to the first temporal circuit 2 aand the second temporal circuit 2 b to respectively receive a firstdetection signal A having a first pulse width T1 and a second detectionsignal B having a second pulse width T2. The subtraction circuit 500includes an operation capacitor Co and cascaded first operationtransistor SWA and second operation transistor SWB, wherein theoperation capacitor Co is connected between the first operationtransistor SWA and the second operation transistor SWB. The firstoperation transistor SWA is used as a switch to control a charginginterval of a first current Ic to charge the operation capacitor Coaccording to the first pulse width T1; and the second operationtransistor SWB is used as a switch to control a discharging interval ofa second current Id to discharge the operation capacitor Co according tothe second pulse width T2, wherein the first current Ic is substantiallyidentical to the second current Id. In this way, the subtraction circuit500 performs the numerical calculation of A-B. It is appreciated thatwhen the subtraction circuit 500 performs the numerical calculation ofB-A, gates of the first operation transistor SWA and the secondoperation transistor SWB receive opposite input signals, e.g.,implemented by using a switching device or a multiplexer.

Please referring to FIG. 6 , it is a circuit diagram of an additioncircuit 600 according to one embodiment of the present disclosure, whichhas two inputs respectively coupled to the first temporal circuit 2 aand the second temporal circuit 2 b to respectively receive a firstdetection signal A having a first pulse width T1 and a second detectionsignal B having a second pulse width T2. The addition circuit 600includes an operation capacitor Co and a first operation transistor SWAand a second operation transistor SWB connected in parallel, wherein theoperation capacitor Co is connected between the first operationtransistor SWA and the second operation transistor SWB. The firstoperation transistor SWA is used as a switch to control a first charginginterval of a first current Ic1 to charge the operation capacitor Coaccording to the first pulse width T1; and the second operationtransistor SWB is used as a switch to control a second charging intervalof a second current Ic2 to charge the operation capacitor Co accordingto the second pulse width T2, wherein the first current Ic1 issubstantially identical to the second current Ic2. In this way, theaddition circuit 600 performs the numerical calculation of A+B.

Referring to FIG. 7 , it is a circuit diagram of an absolute differencecircuit 700 according to one embodiment of the present disclosure, whichhas two input sets respectively coupled to the first temporal circuit 2a and the second temporal circuit 2 b to respectively receive firstdetection signals A and Abar having a first pulse width T1 and seconddetection signals B and Bbar having a second pulse width T2, whereinAbar and Bbar are generated from A and B using the inverter or viceversa. When the first pulse width T1 is larger than the second pulsewidth T2, the first input set (including operation transistors SWA andSWBbar) receives the pulse width signals A and Bbar to control a firstcharging interval of a first current Ic1 to charge the operationcapacitor Co. When first pulse width T1 is smaller than the second pulsewidth T2, the second input set (including operation transistors SWB andSWAbar) receives the pulse width signals B and Abar to control a secondcharging interval of a second current Ic2 to charge the operationcapacitor Co. In this way, the absolute difference circuit 700 performsthe numerical calculation of |A−B|.

Although the current sources in FIGS. 5-7 are shown to be implemented bycontrolling a transistor using a control signal PBIAS, but the presentdisclosure is not limited thereto. Other current sources may be used.

Please referring to FIG. 8 , it is a circuit diagram of a recursivecircuit 800 of a pixel circuit according to one embodiment of thepresent disclosure. The recursive circuit 800 is coupled to theoperation circuit 12 and used to control the operation timing of theoperation circuit 12 and convert the operation result (i.e. chargesstored in the operation capacitor Co) into a pulse width signal againfor the next operation, e.g., the PW output of the recursive circuit 800being coupled to one signal input of the operation circuit 12 as thesignal A or B in FIGS. 5 to 7 .

The recursive circuit 800 includes a first recursive transistor SWr1, asecond recursive transistor SWr2 and a third recursive transistor SWr3,which have identical connection as the first transistor SW1, the secondtransistor SW2 and the third transistor SW3 in FIG. 3 .

In FIG. 8 , the circuit in a dashed block 81 is referred to avoltage-temporal conversion circuit which is used to convert a voltageon the operation capacitor Co to a PW signal similar to A and B, whereinthe operation capacitor Co in FIG. 8 is the operation capacitor Co inFIGS. 5 to 7 .

Please referring to FIG. 9 together, it is an operational timing diagramof the recursive circuit 800 in FIG. 8 . Before the operation capacitorCo starts to perform the numerical calculation on the detection signal Afrom the first temporal circuit 2 a and the second detection signal Bfrom the second temporal circuit 2 b, the operation capacitor Co isreset at first. In the operation reset interval, control signals AZT andBIASr are respectively changed to a high voltage level for resetting avoltage of the operation capacitor Co to V_(AZ). In this aspect, thesecond recursive transistor SWr2 is used as an operation resettransistor so as to reset the voltage of the operation capacitor Co inthe operation reset interval. In the numerical calculation interval(e.g., slant-lines region), the control signal AZr is changed to a lowvoltage level and the operation result of the operation circuit 12 isstored in the operation capacitor Co to change a voltage thereon,wherein magnitude of the voltage change is corresponding to theoperation result. Next, in the charge storage interval, the operationcapacitor Co holds the voltage thereon. Till a next operation starts,the voltage-temporal conversion circuit 81 converts the calculatedvoltage to a PW signal for the operation of the operation circuit 12.The operations of the charge storage interval and the PW convertinterval of the recursive circuit 800 are similar to those of the chargestorage interval and the PW convert interval in FIG. 4A, e.g., using aramp signal to generate the PW signal, and thus details thereof are notrepeated herein.

In one aspect, the recursive circuit 800 further includes an inverterINV to invert a phase of the outputted PW signal. However, when theoperation circuit 12 includes an inverter therein, the recursive circuit800 does not include the inverter INV.

In the present disclosure, the PW convert interval of FIG. 4A as well asthe operation reset interval and the numerical calculation interval ofFIG. 9 as a whole is referred to an operation interval T_(O) herein,wherein the operation reset interval of FIG. 9 is performed in parallelwith or behind the PW convert interval of FIG. 4A.

It is appreciated that if there is no next operation after the recursivecircuit 800, the recursive circuit 800 directly provides (e.g.,controlled by a switching device) the calculated voltage on theoperation capacitor Co to the identify circuit 14 for identification,e.g., compared with a reference voltage using a comparator.

The circuit in FIG. 8 is called recursive circuit because the operationresult of the operation circuit 12 may be stored and then converted to aPW signal multiple times by the recursive circuit 800 to performmultiple recursive operations. That is, the operation circuit 12 notonly calculates the detected result of the photodiode PD, but alsocalculates the operation result thereof with the operation result ofother pixels.

In this way, by using the pixel circuit 200 of FIG. 2 in conjunctionwith the recursive circuit 800 of FIG. 8 , it is possible to performvarious pixel-wise operations on the pixel data for variousapplications. The identify circuit 14 performs various identificationsaccording to a final operation result of the pixel circuit 20 and therecursive circuit 800, e.g., identifying the lift-up of a navigationdevice, calculating the navigation vector, performing image recognition,categorizing images, performing motion detection and performingmulti-layer neural network so as to realize the pixel structure withpixel-wise operation.

For example referring to FIG. 10 , it is a schematic diagram of oneapplication of the pixel circuit of the present disclosure that performsthe motion detection (e.g., adapted to a security system). A pixel arrayof a camera includes multiple pixels arranged in an array. The identifycircuit 14 performs the motion detection according to 9 adjacent pixels,including pixel 0 to pixel 8, wherein the pixel 0 is a central pixel ofpixel 1 to pixel 8. In this aspect, the pixels 0 to 8 respectivelyinclude the pixel circuit 200 in FIG. 2 and/or at least one operationcircuit 12.

As mentioned above, pixels 0 to 8 respectively generate a firstdetection signals A0 to A8 and second detection signals B0 to B8. Afterthe subtraction circuit 500 (e.g., included in the pixel circuit ofpixels 0 to 8, but not limited to) performs the numerical calculation onthe first detection signals A0 to A8 and the second detection signal B0to B8 of the pixels 0 to 8, the subtracted result Y0 to Y8 are obtainedand stored in the corresponding operation capacitor Co (e.g., shown inFIG. 8 ), wherein Y0 to Y8 indicate that each of pixels 0 to 8 performsthe temporal difference operation on detected signals obtained indifferent detection intervals to represent the brightness variationdetected by every pixel.

Next, after converting Y0 to Y8 to PW signals using the recursivecircuit 800, the absolute difference circuit 700 performs the numericalcalculation of absolute differencing between Y0 and Y1, Y0 and Y2 . . .Y0 and Y8 to obtain Y01 to Y08, wherein Y01 to Y08 indicate that thepixel array performs the spatial difference operation between differentpixels, and Y01 to Y08 contain the operation result of both the temporaldifference and spatial difference.

Finally, Y01 to Y08 are summed by the addition circuit 600. Similarly,Y01 to Y08 are firstly stored in the corresponding operation capacitorCo, and then converted to PW signals by the voltage-temporal conversioncircuit 81 for the summation of the addition circuit 600.

In one aspect, the addition circuit 600 includes two inputs as shown inFIG. 6 , and the addition circuit each time performs the summation oftwo of Y01 to Y08 that is stored and voltage-temporal converted, andthen summed with another one of the rest of Y01 to Y08 till all of Y01to Y08 is added together.

In another aspect, the addition circuit includes 8 inputs and uses thepulse widths associated with Y01 to Y08 to control the chargingintervals of respective current sources as a way of adding Y01 to Y08together.

The identify circuit 14 receives a summation of the addition circuit600, and compares the summation with a predetermined threshold (e.g.,using a comparator). When the summation of Y01 to Y08 is larger than orequal to the predetermined threshold, it means that a motion isdetected. The identify circuit 14 then outputs a control signal toperform corresponding controls, e.g., turning on a light source,starting to record images or increasing image capture frequency.

In another aspect, the identify circuit 14 receives a summation of thetemporal differences Y0 to Y8 (e.g., Y0 to Y8 directly outputted to theaddition circuit 600 from pixels 0 to 8). When the summation is largerthan or smaller than (determined according to the light sourcearrangement) a brightness threshold, it means that a mouse device islifted up by a user.

It is appreciated that although FIG. 10 uses 9 neighboring pixels todetect the temporal and spatial brightness variation to perform themotion detection or lift-up detection, the present disclosure is notlimited thereto. The identify circuit 14 uses a proper number of pixelsto detect the temporal and spatial brightness variation, e.g., theproper number being determined according to environment to be detectedand a size of pixel array.

As mentioned above, in the conventional optical sensor, pixel data isconverted to digital data at first, and then the digital data isoperated by the digital backend such that frame buffers are required totemporarily store frame data. Accordingly, the present disclosurefurther provides a pixel circuit that outputs pulse width signals forthe analog operation (e.g., FIG. 2 and FIGS. 5 to 7 ). The pixel circuitoutputs, within an operation interval, the PW signals corresponding todifferent detecting intervals for the analog operation of an operationcircuit so as to realize the objective of the pixel-wise operation ofpixel data.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A pixel circuit, comprising: a photodiode; and atemporal circuit, coupled to the photodiode and comprising: a capacitor,having a first end coupled to the photodiode; a first transistor, asource thereof being connected to a voltage source and a drain thereofbeing connected to a node; a second transistor, coupled between a secondend of the capacitor and the node; and a third transistor, coupledbetween the node and a ground voltage, and a controlled terminal thereofbeing coupled to the second end of the capacitor.
 2. The pixel circuitas claimed in claim 1, further comprising a reset transistor coupledbetween the photodiode, the temporal circuit and the voltage source, andconfigured to reset the temporal circuit.
 3. The pixel circuit asclaimed in claim 1, wherein a controlled terminal of the firsttransistor is configured to receive a ramp signal for converting energystored in the capacitor to a detection signal.
 4. The pixel circuit asclaimed in claim 3, wherein a pulse width of the detection signal ispositively related to the energy.
 5. The pixel circuit as claimed inclaim 1, further comprising a transfer transistor connected between thephotodiode and the temporal circuit.
 6. The pixel circuit as claimed inclaim 1, further comprising an inverter connected behind the node.
 7. Anoptical sensor, comprising: a photodiode, configured to generate lightenergy; and a first temporal circuit and a second temporal circuit, bothcoupled to the photodiode and respectively configured to store the lightenergy within different time intervals, each of the first temporalcircuit and the second temporal circuit comprising: a capacitor, havinga first end coupled to the photodiode; a first transistor, coupledbetween a voltage source and a node, and a controlled terminal of thefirst transistor is configured to receive a control signal forconverting the light energy stored in the capacitor to a detectionsignal; a second transistor, coupled between the node and a second endof the capacitor; and a third transistor, coupled between the node and aground voltage, and a controlled terminal thereof being connected to thesecond end of the capacitor.
 8. The optical sensor as claimed in claim7, wherein the first temporal circuit and the second temporal circuitare respectively configured to output the detection signal within thesame operation interval.
 9. The optical sensor as claimed in claim 7,further comprising a transfer transistor connected between thephotodiode and the first and second temporal circuits.
 10. The opticalsensor as claimed in claim 7, further comprising a reset transistorconfigured to reset the first temporal circuit and the second temporalcircuit within the different time intervals.
 11. The optical sensor asclaimed in claim 7, wherein each of the first temporal circuit and thesecond temporal circuit further comprises an inverter connected behindthe node.
 12. The optical sensor as claimed in claim 7, wherein thesecond transistors of the first temporal circuit and the second temporalcircuit are not conducted simultaneously within the different timeintervals.
 13. The optical sensor as claimed in claim 7, wherein thecontrol signal is a ramp signal.
 14. An optical sensor, comprising: aphotodiode, configured to generate light energy; and a first temporalcircuit and a second temporal circuit, both coupled to the photodiodeand respectively configured to convert the light energy within differenttime intervals to pulse width signals, each of the first temporalcircuit and the second temporal circuit comprising: a capacitor, havinga first end coupled to the photodiode; a first transistor, a sourcethereof being connected to a voltage source and a drain thereof beingconnected to a node; a second transistor, coupled between the node and asecond end of the capacitor; and a third transistor, coupled between thenode and a ground voltage, and a controlled terminal thereof beingconnected to the second end of the capacitor.
 15. The optical sensor asclaimed in claim 14, wherein the first temporal circuit and the secondtemporal circuit are respectively configured to output a detectionsignal, converted from the light energy, within the same operationinterval.
 16. The optical sensor as claimed in claim 14, furthercomprising a transfer transistor connected between the photodiode andthe first and second temporal circuits.
 17. The optical sensor asclaimed in claim 14, further comprising a reset transistor configured toreset the first temporal circuit and the second temporal circuit withinthe different time intervals.
 18. The optical sensor as claimed in claim14, wherein each of the first temporal circuit and the second temporalcircuit further comprises an inverter connected behind the node.
 19. Theoptical sensor as claimed in claim 14, wherein the second transistors ofthe first temporal circuit and the second temporal circuit are notconducted simultaneously within the different time intervals.
 20. Theoptical sensor as claimed in claim 15, wherein controlled terminals ofthe first transistor of the first temporal circuit and the secondtemporal circuit are respectively configured to receive a ramp signalfor converting the light energy to the detection signal.